Hypothyroidism vs Hyperthyroidism

[RoughCollies]

Hypothyroid / hypothyroidism dogs are more common in certain breeds. Hypothyroid / hypothyroidism of dogs occurs in middle age. Lack of secretion of TSH from the thyroid gland in the neck of dogs is responsible for hypothyroidism. Hypothyroidism runs in families of dogs. In some cases, hypothyroidism of dogs is an immune mediated disease. Once the thyroid gland of dogs becomes defficient in thyroid hormone production the dog developes hypothyroidism. The supplementation of thyroid hormone or levothyroxin cures hypothyroidism in dogs. Hypothyroid dogs must take thyroid hormone for the rest of their lives. Hypothyroidism of dogs is a relatively benign disease. Hypothyroid dogs are often overweight.

A sluggish thyroid gland or hypothyroidism is the commonest endocrine gland disease of dogs. I often diagnose this condition when a pet reaches four to six years of age. Male and female dogs are equally affected but I have noticed that neutered animals are more susceptible than intact pets. The thyroid gland consists of two lobes located at the base of the neck. This gland produces thyroxine, a hormone that regulates the body’s metabolic rate, that is the rate at which it burns calories. When thyroxine is not produced in sufficient quantity a number of things happen.

It is common for dogs with hypothyroidism to gain weight while only eating moderately. These dogs have been described as “easy keepers” because they gain weight so easily. Not withstanding, the majority of plump and fat dogs do not have thyroid disease – they just eat too much and get too little exercise. Many owners are oblivious to weight gain in their pets. But when an animal’s backs become flattened instead of curved and they huff and puff with every exertion some owners bring them in for a check up. I run thyroid tests on all these dogs. Most cases of hypothyroidism stem from the dog’s own immune system attacking thyroid gland tissue. This condition is called autoimmune thyroiditis. Common hypothyroidism is further broken down into two types, lymphocytic thyroiditis and idiopathic thyroid atrophy. In both cases, the gland fails to produce enough of the hormone, thyroxine. The signs and treatment are the same.


Hair and Skin Changes
Adequate levels of thyroid hormone are necessary for hair to grow. When hormone levels are low, hair growth sparsely over the lumbar area equally on both sides. The back of the rear legs is also commonly affected. The pet’s hair coat is often scurfy, flaky and dull. The coat commonly lacks finer body hairs and undercoat. The tail may be bald as a rat’s tail. An important clue pointing to thyroid deficiency is that this hair loss is not itchy as it would be from fleas , allergic skin or infectious skin disease. Hypothyroid dogs commonly have excess black pigment in the skin of their groin. This pigment results in a condition called acanthosis nigricans. Sometimes this pigment is present over much of the body and the skin becomes oily and thickened. Broken toenails and toenail infections are common. Hair coat color may change.

Infertility
Female dogs with hypothyroidism often cycle erratically. When they do pass through estrus or heat, they are often infertile. Pseudopregnancy or false pregnancy with milk flow and abdominal distension is common in these dogs (especially dachshunds). Male dogs may have low sperm levels and decreased libido.


Breeds Commonly Affected
I see Hypothyroidism most commonly in Labrador and Golden Retrievers, Dachshunds, Cocker Spaniels, Boxers Doberman Pinchers and Greyhounds in that order of frequency. I rarely encounter this disease in terriers og
Sr other small breeds and I have never encountered it in giant breeds.


Other Recognized Signs of Hypothyroidism

ome other symptoms of sluggish thyroid function are seen occasionally and are seen with a number of diseases that are not related to the thyroid gland. These symptoms include mental dullness or depression, cold intolerance, slow heart rate, constipation, anemia, muscle weakness and atrophy, nerve disturbances, edema, stunted growth, and slowed clotting of the blood. Hypothyroid dogs have more than their fair share of joint pain and swelling and ear and skin infections. Lethargic behavior – such as increased sleeping, less play activity and easy fatigue may also indicate thyroid disease. It has also been reported that hypothyroid dogs have more “dry eye” disease (keratoconjunctivitis sica) but I have never seen a case.


Laboratory Diagnosis of Hypothyroidism
When I recognize one or more of the signs I have mentioned, I draw blood for thyroid function tests. The blood I remove is often creamy whitish in color due to the presence of large amounts of fats (triglycerides and cholesterol) in the blood of hypothyroid animals. I have the blood analyzed for thyroid hormones (T-4, free T-4 and T-3). I will occasionally also run at thyroglobin autoantibody test to determine if autoimmune thyroid disease is present. Low hormone levels in the absence of signs of other diseases are diagnostic of hypothyroidism. Blood levels of T-4 are normally 1.0-4.0 micrograms/deciliter. Normal levels of T-3 are 45-150 nanograms/decileter and normal levels of Free T-4 are 11-43 picomols/leter. I become suspicious of hypothyroidism when the numbers for T-4 hover about one unit and T-3 and Free T-4 levels are low-normal - even if the lab reports the case as normal. Falsely low thyroid hormone levels can be due to administration of steroids (cortisone) or concurrent systemic disease. A TSH stimulation test can be run if the diagnosis is in doubt.


Treatment
Fortunately, thyroid hormone is easily synthesized and available in inexpensive tablet form. I generally prescribe the T-4 form of the hormone, l-thyroxine (levothyroxine sodium). We begin by administering 10 micrograms per pound of body weight (0.lmg/10 lbs) twice a day. Borderline dogs are best put on thyroid hormone for a sixty-day trial. This beginning dose is only an estimate. All dogs need their dose individually tailored to their needs. Signs that the initial dose may be too high are agitation, excessive thirst, and diarrhea. When these occur I lower the dose. Thirty days after beginning treatment I assay a second blood sample for Free T-4. If levels are still not adequate the dose is increased. I then retest the dog every six months. Once a dog is placed on medication, it should be given for the rest of the pet’s life.
Hypothyroidism runs in families so it is unwise to breed hypothyroid dogs or their normal littermates. When the disease is diagnosed early and treated one can expect the pet to live a long and happy life

[RoughCollies]

Clinical Signs of Hypothyroidism

When the rate of metabolism slows down, virtually every organ in the body is affected in some manner. Most affected dogs have one or more of several "typical" physical and/or chemical abnormalities. These include:

(a) Weight gain without an increase in appetite

(b) Lethargy and lack of desire to exercise

(c) Cold intolerance (gets cold easily)

(d) Dry haircoat with excessive shedding

(e) Very thin haircoat to near baldness

(f) Increased pigmentation in the skin

(g) Increased susceptibility to skin and ear infections

(h) Failure to re-grow hair after clipping or shaving

(i) High blood cholesterol

Some dogs also have other abnormalities that are not the typical findings. These include:

(a) Thickening of the facial skin so they have a "tragic facial expression"

(b) Abnormal function of nerves causing non-painful lameness, dragging of feet, lack of co-ordination, and a head tilt

(c) Loss of libido and infertility in intact males

(d) Lack of heat periods, infertility, and abortion in females

(e) Fat deposits in the corneas of the eyes

(f) Keratoconjunctivitis sicca or so-called "dry eye" due to lack of proper tear production

[RoughCollies]

It's rare to see hyperthyroidism in dogs, compared to the rate of hypothyroidism. It does happen however.

Hyperthyroidism

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Excessive secretion of the thyroid hormones, T4 and T3, results in signs that reflect an increased metabolic rate and produces clinical hyperthyroidism. It is most common in middle-aged to old cats but also develops rarely in dogs.

Functional thyroid adenoma (adenomatous hyperplasia) is the most common cause of feline hyperthyroidism; in ~70% of cases, both thyroid lobes are enlarged. Thyroid carcinoma, the primary cause of hyperthyroidism in dogs, is rare in cats (1-2% of hyperthyroidism cases).

Clinical Findings and Diagnosis: The most common signs include weight loss, increased appetite, hyperexcitability, polydipsia, polyuria, and palpable enlargement of the thyroid gland. GI signs are also common and may include vomiting, diarrhea, and increased volume of feces. Cardiovascular signs include tachycardia, systolic murmurs, dyspnea, cardiomegaly, and congestive heart failure. Of hyperthyroid cats, 5-10% exhibit apathetic signs (eg, anorexia, lethargy, and depression); weight loss is common.

High serum concentrations of T4 and T3 confirm the diagnosis; however, they are subject to a wide degree of fluctuation, and more than one basal measurement may be necessary.


Treatment: Spontaneous hyperthyroidism can be treated by thyroidectomy, radioiodine therapy, or chronic administration of an antithyroid drug. With unilateral thyroid tumors, hemithyroidectomy corrects the hyperthyroid state, and thyroxine supplementation usually is not necessary. For bilateral thyroid tumors, complete thyroidectomy is indicated, but parathyroid function must be preserved to avoid postoperative hypocalcemia. Thyroxine supplementation should be started 1-2 days after complete thyroidectomy. If iatrogenic hypoparathyroidism develops, treatment with vitamin D and calcium is also indicated.

Radioactive iodine provides a simple and safe treatment. Radioiodine is concentrated within the thyroid gland and selectively irradiates and destroys hyperfunctioning thyroid tissue. The main disadvantage of such therapy is that most practitioners do not have access to radioiodine.

Treatment with methimazole, an antithyroid drug, controls hyperthyroidism by blocking thyroid hormone synthesis. The recommended initial daily dose of methimazole is 10-15 mg in two or three divided doses. The dose is adjusted to maintain circulating thyroid hormone concentrations within the normal range, and the drug is given daily. Adverse side effects, the more serious of which are agranulocytosis and thrombocytopenia, develop in <5% of treated cats. If this occurs, methimazole should be discontinued and supportive therapy instituted; these adverse reactions should resolve within 2 wk. To maintain normal levels of thyroid hormone and to monitor for adverse reactions during the first 3 mo of treatment (when the most serious side effects associated with methimazole therapy develop), complete blood counts and serum thyroid hormone determinations should be repeated at 2- to 4-wk intervals, and the drug dose adjusted as necessary. Subsequently, serum T4 concentrations should be measured at 3- to 6-mo intervals to monitor dosage requirements and response to treatment. Propylthiouracil, another antithyroid drug, is not recommended for use in cats because of the high incidence of serious side effects (especially hemolytic anemia and thrombocytopenia).

[Dignity]

Oh oh oh - I wanted to add something . Thyroid problems are often genetic (if the dog's parents have it, the dog is going to have a higher chance of having it). If your adopted your dog from a breeder and it does happen to have a thyroid problem, you should let the breeder know.

I didn't see that listed in the posting, but maybe I just missed it.

[Dobified]

I posted this trhead a while back :

http://www.prodoggroomingsupplies.co...ad.php?t=11486